The present invention relates generally to the formation of endless conveyor belts and, more particularly, to the formation of butt-type splices between two conveyor belt ends.
Rubber or PVC based conveyor belts have many and varied industrial applications. Typically, such conveyor belts are of a substantially flat open-width laminated construction comprised of an intermediate carcass layer having a carry cover bonded coextensively to one face thereof and a pulley cover bonded coextensively to the opposite face thereof to form a composite trilaminate belting material. The pulley cover forms the inward surface of the belting, i.e., the surface which will contact pulleys and other guiding and support structure in the operational end usage of the belting, while the carry cover forms the outward surface of the belting which will be exposed for transport of materials thereon or other end use functions of the belting.
In many, if not most, uses of such conveyor belts, an elongate length or lengths of the belting are connected end-to-end with one another to produce a continuous conveyor belt. The connection of belt ends to one another can be accomplished in various manners, one commonly preferred means of connection being to adhesively splice belt ends together in an end-abutting relationship whereby the splice area is substantially comparable in cross-sectional dimension and operability to the remaining lengthwise extent of the overall belt. Typically, such a so-called butt splice is produced by initially cutting the belt ends to be connected along parallel diagonal lines for precise end edge abutment and then cutting away the carry and pulley covers from each belt end to form diagonal recesses on each opposite side of the belt ends when abutted. Preferably, the carry cover side of each belt end is cut away to a greater extent than the pulley side so that when the prepared belt ends are abutted the recess formed at the carry cover side is larger lengthwise with respect to the belts than the recess formed on the pulley cover side. The thusly prepared belt ends are then adhesively joined in end-abutting relation by cementing or otherwise adhering a piece of splicing material and a covering insert member into the recesses at each opposite side of the abutted belt ends so as to overlap the exposed intermediate carcass layer of each belt end, commonly referred to as a "scab." The splicing material and the covering insert member are cut to correspond substantially in shape to the respective recesses. The covering insert member commonly is of substantially the same material as the carry and pulley covers of the belting. The splicing material utilized in the recess at the pulley cover side of the abutted belt ends is typically an adhesive-backed so-called breaker strip, while the splicing material typically utilized in the recess at the carry cover side of the belt ends is typically a textile fabric.
Since the carry cover side of the conveyor belt faces outwardly in its normal operation and thereby is subjected to greater stress and strain, e.g., when traveling through a change of direction about a supporting pulley, it is important that the portion of a splice at the carry cover side of abutted belt ends have appropriate strength, flexibility and elongational properties to withstand normal operation of the belt. A primary factor determining these properties of a belt splice is the splice fabric utilized in the recess on the carry cover side of a belt splice. Ideally, the splice fabric should have relatively high tensile strength yet be relatively flexible and be stretchable only to a limited extent sufficient to accommodate elongational forces to which the conveyor belt is typically subjected. At the same time, the fabric thickness should be minimized so that the overall thickness of the belt is not increased at splice locations.
No known fabric meets all of these properties. Instead, conventional splice fabrics represent a compromise of the optimal combination of properties. One of the most common conventional splice fabrics currently in use is a woven fabric formed of a set of relatively high denier nylon warp yarns held in a substantially linear orientation by filling yarns at each opposite side of the nylon warp yarns intermeshed with a second set of relatively low denier binder warp yarns. While nylon is of a relatively lower tenacity and relatively lower modulus of elasticity than other known textile yarns, this woven structure, particularly, the linear orientation of the nylon warp yarns, minimizes the stretchability of the fabric and it generally maximizes the fabric tenacity per unit fabric thickness possible with use of nylon yarns while maintaining a sufficient degree of warpwise flexibility in the fabric for use in conveyor belt splices. Disadvantageously, however, such fabrics are nevertheless relatively thick due to the high denier of the nylon warp necessary to achieve an acceptable minimal level of fabric strength, in comparison to the fabric thickness which would be produced by the same fabric construction if a lower denier yarn of higher tenacity were to be used, e.g., polyester yarn. Unfortunately, attempts to use such polyester yarn fabrics in conveyor belt splices to overcome the deficiencies of conventional nylon splicing fabrics have not been successful because the fabric construction coupled with the high tenacity and high modulus of elasticity of polyester yarns gives the fabric such a high modulus of elasticity that the fabric exhibits a tendency to separate from the spliced belt ends under operational stresses. Accordingly, conventional wisdom has developed that conventional yarns of a high modulus of elasticity, which typically also exhibit a high tenacity, are unsuitable for use in conventional splicing fabric construction.